HP catalyst killer

ABSTRACT

A process for preparing olefinic polymers by metallocene catalyzed olefin polymerisation in which at least one volatile catalyst kill agent is introduced. A non-volatile catalyst kill agent may also be used in conjunction with the volatile catalyst kill agent. Water may be used as the volatile agent and compounds containing a terminal hydroxy group, oxygen, nitrogen or sulfur may constitute the non-volatile agent. Purified monomer is recycled to the reactor.

FIELD OF INVENTION

The invention relates to processes for polymerizing olefins usingmetallocenes and in particular to catalyst killing systems for use insuch processes. The term catalyst killing refers to the deactivation ofthe catalyst. The deactivation may be a partial or complete suppressionof polymerisation appropriate to enable the overall process to beperformed in a stable manner.

BACKGROUND OF THE INVENTION

It is known to use low molecular weight gases or liquids in order tokill Ziegler-Natta catalyst systems to reduce the catalyst systemactivity to a level where the polymerisation stops. Ziegler-Nattacatalyst systems usually employ a titanium chloride transition metalcomponent and an aluminum alkyl co-catalyst component or activator.

EP 116917 (Ruhrchemie) for example describes a killer of CO₂ andalcohols. These products are said to react with catalyst to formnon-volatile compounds, not active in polymerization.

The use of water as a Ziegler-Natta catalyst killer is disclosed in U.S.Pat. No. 4,701,489 (El Paso). However whilst water is a known effectivecatalyst killer, acid may evolve and at high levels corrosion may becaused.

It is also known to use high molecular weight products (polyglycols;epoxides; ethylene copolymers; organic titanium compounds;alkoxysilanes; peroxides; zeolites as a water carrier; or surface-activeagents) as Ziegler-Natta catalyst killers.

EP 162274 (Ruhrchemie) discloses a high pressure Ziegler-Natta catalyzedpolymerization process involving deactivation with an oxygen-containingwaxy ethylene copolymer. The purpose is to prevent polymerization ofresidual monomer in the separator and gas circulating system. EP 140131(Ruhrchemie) uses polyglycols for similar purposes.

DE-3322329 (Mitsubishi Petrochemical) discloses killers of peroxideswhich break up into a complex mixture of volatile CO₂ and other mainlyvolatile components.

It is further more known from JP-A-57158206 (Sumitomo) to use in aslurry polymerization process a mixture of water, sorbitan alkyl ester,and an aliphatic C₃ -C₈ hydrocarbon as catalyst killer to avoid use of alarge amount of water, presumably by using the sorbitan alkyl ester toemulsify the water in the C₃ -C₈ solvent. EP-B-71252 (Sumitomo)discloses use of a suspension of water containing fatty acid salt in ahydrocarbon for a similar purpose. The fatty acid salt may act toneutralise acids formed by the water-catalyst reaction.

In recent years use of metallocene based polymerisation catalyst systemsusing metallocenes as the transition metal component has been suggested;generally using alumoxane as a cocatalyst. For the purpose of this textthe term Ziegler-Natta catalyst systems is used to excludemetallocene/alumoxane systems. The metallocene based systems employrelatively small, molecules of generally unsupported (particularly inhigh pressure processes) metallocene transition metal components whichcan have a significant, although still low, vapor pressure at conditionsfor separation of polymer and unreacted monomer. The cocatalyst hasgenerally a much higher molecular weight than conventional aluminumalkylcocatalysts and may be an alumoxane as afore mentioned or other suitablecocatalyst complex. However these compounds may still have anappreciable vapor pressure at separation conditions. Often thecocatalyst is used in great excess over the metallocene but the overallcatalyst system has a high activity so that catalyst concentrations canbe low.

EP-35242 (BASF) uses methanol as a catalyst killer for suchmetallocene/alumoxane systems; DE 3127133 (Hoechst) uses n-butanol.

Metallocene/alumoxane based catalyst systems have been proposed in whichwater is introduced into the polymerization zone to create alumoxane insitu (See DE 2608933 Kaminsky; Exxon EP 308177). EP 308177 (Exxon) useswater in the monomer feed to activate, not deactivate, TMA separatelyintroduced as part of the catalyst system.

EP 328348 (Mitsui Petrochemical) uses water in addition to alumoxane andoptionally an organoaluminum compound to improve catalysis in lowpressure conditions with water (See Example 1 of EP 328348) used to killcatalyst activity. However no elevated pressure is used and there is norecycling because the polymerisation in Example 1 is a batch procedure.

These metallocene based catalyst systems may be used in high pressurepolymerisation (See EP 260999 and DE 3150270) including continuousprocesses involving a recycling and recompression of unreacted monomer.

In industrial-scale high pressure polymerisation a monomer feed issupplied continuously by a compressor installation, polymerised underpressure in a tubular or autoclave reactor, then removed and supplied toa separation stage which may involve high and low pressure separationwhereupon polymer is isolated and unreacted monomer is recycled. Theextent of recycling can vary depending on the reactivity and amount ofcomonomers.

The killing of metallocene based catalyst systems in elevated pressuresystems with recycled monomer streams may be especially critical.Residual catalyst activity may occur in the separation and in therecycle system; catalyst activity may be highly sensitive to residualkiller present in polymerisation. The amount of catalyst system andkiller injected need to be appropriately controlled.

It is the object of the invention to provide a commercially viablecatalyst killing technology to provide sustained, controllablepolymerization with high activity metallocene catalyst systems in fluidsystems such as high pressure polymerisation. .It is a further object tomaintain the specific advantages of metallocene catalyst systems such asthe capability of producing narrow molecular weight distribution (MWD),and/or narrow compositional distribution (CD) of the polymer productsand high productivity of the catalyst system.

In particular it is amongst the objects of the invention to provide acatalyst killing technology which provides a quick killing reaction;reduces or avoids polymerization in the high pressure separator stage,and reduces or avoids polymerization of the monomer during recycle. Itis furthermore amongst the objects to reduce and minimise suppression ofthe polymerization reaction resulting from carry over of the killercomponents in the recycled feed to the reactor. It is also one of thepossible objects to provide a killer system which can be adapted easilyto varying process requirements for producing different polymers ofdifferent molecular weights as well as different comonomer types andcontent at different polymerisation and elevated pressure separationconditions whilst making efficient use of the catalyst system.

SUMMARY OF THE INVENTION

The invention is related to processes for preparing olefinic polymersincluding the steps of:

(a) continuously feeding olefinic monomer and a catalyst system of ametallocene component and a cocatalyst component to a reactor;

(b) continuously polymerising the monomer in a polymerisation zone inthe reactor under elevated pressure;

(c) continuously removing a monomer/polymer mixture from the reactor;

(d) continuously separating monomer from molten polymer at a reducedpressure to form a monomer-rich and a polymer-rich phase; and

(e) recycling separated monomer to the reactor.

The term "olefinic monomer" includes generically copolymerisablemonomers or blends of two or more olefins or diolefins or polyolefins aswell as monomer feeds consisting substantially of one olefin. The termis used herein to include all compounds capable of additionpolymerisation or copolymerisable with ethylene such as cyclic olefin;norbornenes; styrene, alkyl substituted styrenes and vinylsilanes.

The recycling is advantageously direct that is to say the monomer-richphase is returned to the polymerization zone without the necessity ofadditional separation or purification steps.

In a first aspect of the invention there is used in combination with theprocess set out above, both a volatile killer component and anon-volatile catalyst system killer component. The terms volatile andnon-volatile are used in the context of the separation conditions. Thevolatile component may tend to predominate in the phase to be recycled;the non-volatile killer components tends to concentrate predominantly inthe polymer. The separation of polymer; oligomer and monomer is notperfect. The volatile killer components will also be present in thepolymer to some degree at separation for example perhaps by entrainmentby the heavy component. By using the killer components polymerisationactivity in the polymer phase can be suppressed. The volatile componentflow rate can be adjusted easily to achieve the dual objective of (a)suppressing polymerisation in the recycle and (b) avoiding unduereductions in catalyst activity in polymerisation.

Advantageously the non-volatile component is non-decomposable andthermally stable at the separating conditions to avoid unpredictableentrainment of residues in the recycle.

Preferably the non-volatile killer component is added in a ratio of from0.01 to 10 moles of non-volatile killer component per mol of metal(metallocene and cocatalyst), preferably from 0.05 to 2. Thenon-volatile killer component may however also consist of or comprisecompounds which are decomposable and for example release bydisassociation an oxygen containing compound, preferably a compoundcontaining terminal hydroxy groups to provide a killing action.

Preferably the volatile killer component is thermally stable atseparating and recycle conditions so that only a single volatile speciesis present whose behaviour is predictable.

The volatile killer component may be water. The term "water" as usedherein also covers compounds which can decompose to yield water such ashydrogen peroxide and analogous isotope derived materials such as D₂ O(deuteriumoxide). Advantageously the volatile and non-volatilecomponents are admixed for common introduction into the reactor effluentstreams, preferably in the form of a solution or micro-emulsion whichmay be formed with the aid of additional solvent.

Suitably at least the volatile component is added in a killer reactionzone upstream of a high pressure let-down valve although it may also beadded downstream.

In a second aspect applicable to the general aspect (a) to (e) provides,in combination with the process set out above, the addition of water asa volatile killer component. Water may possibly be added in amountswhich are equal to or preferably exceed those needed to kill residualcatalyst activity in the recycle and so may be dosed in a greater rangeof concentrations and/or be effective to kill the catalyst system in theseparated polymer at least to some extent. Water may be used inappropriate circumstances without using a non-volatile killer component.The term "water" also includes precursor and isotope equivalents such asH₂ O₂ and D₂ O as discussed above.

It is believed that water used in excess acts an effective catalystkiller but, when water residue re-enters the reactor and is present in amuch lower proportion relative to newly introduced catalyst system,water has little negative or may even have a positive effect on catalystsystem productivity. Formation of hydrogen chloride or of othercorrosive chlorine compounds can be kept low as the amounts of waterused are low. The water which is in excess to that needed to react withalumoxane may have different beneficial effects which reflect inpreserved or apparent increased productivity. The following representpossible hypotheses for these surprising beneficial effects. Excesswater may react with surplus volatile TMA contained in commercial methylalumoxane to make additional cocatalytically active or inactive product.Excess water may also gradually react with other impurities includingalkylaluminum to provide reaction products which can be more easilyrendered non-volatile and purged from the system.

It is hence believed that the volatile and/or non-volatile killerscavenges volatile catalyst and cocatalyst components and reducesconsequential undesirable modification of the catalyst activity afterrecycling of such components.

Preferably the cocatalyst component includes an aluminum alkyl capableof hydrolysing with excess water to produce alumoxane. The aluminumalkyl may be trimethyl aluminum present in catalyst systems. Thus thereaction product not only removes water but may produce additionalmaterial which is catalytically useful. The catalyst system may alsoinclude alumoxane formed prior to injection into the polymerisation.

Suitably there is additionally added a non-volatile killer componentalthough in certain process configurations water may be used on its own.

The elevated polymerisation pressure for high pressure processes of theinvention may be from 50 to 3500 bar, preferably from 300 to 2000 barand especially from 500 and advantageously from 800 to 1600 bar.Polymerisation may be at a temperature of from 50 to 350° C., preferablyfrom 80° C. to 250° C. and especially from 120° C. to 220° C. It ispreferably at least 20° C., especially at least 30° C. above the meltingpoint of the resulting polymer.

The ranges may cover a wide variety of process configurations and rawmaterials but in each case suitably the process configuration includes asystem for directly recycling unreacted monomer, preferably withoutpassing through an additional scavenging step for removing poisonsincluding poisons resulting from unreacted killer component or killerresidues.

Preferably water is added in amounts such that the catalyst system iskilled sufficiently to permit polymer separation without overheating ofseparated polymer by residual polymerisation activity, unreacted waterbeing recycled with separated, unreacted monomer. Additionally thecatalyst system may contain a component capable of reacting withunreacted water. Advantageously water is added into a killer reactionzone upstream of a high pressure let-down valve and the killer reactionzone is defined by a baffle in a high pressure reaction vessel with oneor more polymerisation zones upstream of the killing reaction zone.Preferably monomer and residual water is removed from a low pressureseparator and recycled without additional separate water removal fromthe low pressure separator for feeding to the reactor.

DETAILED DESCRIPTION OF INVENTION

Preferably the metallocene is fed in an amount of from 0.01 to 100 g ofmetallocene per 10⁶ g of total monomer, preferably from 0.1 to 25 oreven 50 g/10⁶ g of polymer and especially from less than 5 g/10⁶. Theinverse of this ratio may be referred to herein as the metalloceneactivity. In high pressure polymerisation conversion of monomer topolymer is usually from 10 to 20%. Actual amounts of metallocene usedare also influenced by the ratio of metallocene (TM) to cocatalyst (Al),usually methylalumoxane. At high Al/TM mol ratio's, the amount ofmetallocenes used may be lower. The amount is also influenced by thetype of metallocene selected which may be influenced by desiredcomonomer incorporation and molecular weight. Typical Al/TM mol ratio's,depending on process needs, for the aforementioned activities are from100 to 10,000.

Advantageously volatile killer is added in a ratio of 0.005 to 2.5 molesof volatile killer per mol of total metal in the catalyst system,preferably from 0.05 to 1.5 and especially from 0.1 to 1.2.

The killer component proportions can be adapted having regard to thephysical process layout and having regard to the metallocene activitywhich typically varies from 10000 (ten thousand) to 5000000 (fivemillion) grams of polymer product per gram of transition metal compoundin the metallocene at an aluminum/transition metal mol ratio of 1000,especially from 50000 (fifty thousand) to 2000000 (two million). Theamount and type of comonomer present may also influence the amount ofthe killer components used.

The optimum levels of each component are to be determined experimentallyfor each polymerisation and product/monomer separation condition andcocatalyst composition.

The rate of addition of the volatile component normally can be elevatedto exceed that needed to kill the catalyst system without depressing themetallocene activity. It can be maximized in a way such that just aminor decrease of catalyst activity due to recycling killer is observedwhereupon the killer level is reduced slightly. This ensures thepresence of a sufficient amount of killer in the monomer recycle system.With the killer system used in the invention, excessive uncontrolledsuppression of catalyst system activity can be avoided, particularly byreducing the above determined amount of killer by from 10 to 20 wt %from the level at which a minor decrease of catalyst activity isobserved for continuous operation, combining in this way adequatekilling with high catalyst activity.

The rate of addition of the non-volatile component (if used) isminimized in order to keep the killer residues in the product as low aspossible. Higher dosing rates may be permissible or even desirable,however, for certain products or for certain product/killer combinationsin cases where the killer components contribute to special productproperties.

Volatile components for use in combination with non-volatile killercomponents may be for instance low molecular weight components with amolecular weight of less than 200, preferentially less than 80,containing reactive O, N or S moiety, such as H₂ O, CO₂, CO, NH₃, SO₂,SO₃, N₂ O; alcohols, diols and triols, ethers, aldehydes, ketones,carboxylic acids and diacids, their anhydrides or esters; amines, amidesor imides or hydrogen peroxide, alkyl hydroperoxides. As indicated abovethe volatile components may be derived by decomposition (such as that ofH₂ O₂) which are themselves volatile.

The volatile components could also include decomposition products ofhigh molecular weight components which can decompose thermally orchemically forming low molecular weight species but this is notpreferred. Examples are peroxides, peresters, peroxydicarbonates,percetals, alkyl-hydroperoxides, hydroperoxides; azo compounds such asazo dicarbonamide, azo-bis-isobutyronitrile, azo-bis-dimethylvaleronitrile; or inorganic components such as ammonium carbonate andammonium hydrogen carbonate.

Components with a half lifetime at reaction conditions of >1 sec may bedecomposed prior to injection by preheating or chemical treatment.

The non-volatile killer components may be a component containingreactive O, N or S--moiety typically with a molecular weight higher than200, preferentially higher than 300. Such oxygen components may be highmolecular weight alcohols, phenols diols, polyols, saccharides, ethers,epoxides, aldehydes, ketones, carboxylic acids, diacids and polyacids,their anhydrides, esters or salts, polyalkylene glycols such aspolyethylene glycol, amines. As indicated they should preferably bestable, but could also include decomposable compounds such as alkylhydroperoxides, peroxy acids or peroxides with halflife times higherthan 1 min. at reaction conditions. Further reactive alkoxy silanes orsiloxanes may be used such as tetraethoxysilane or silanol terminatedsiloxanes (silicon oils). Nitrogen components which may be used includefor example high molecular weight amines, imides and amides such asoleoamide and erucamide and their reaction products with alcohols,carboxylic acids or their anhydrides. Examples of sulfur compounds arethiols or polythiols. The non-volatile component further may be ananorganic compound with a high oxidizing power such as permanganates orchlorates.

Preferably the non-volatile killer component is an oxygen or nitrogencontaining compound, especially a compound containing at least onelabile hydrogen such as a terminal hydroxy group. The terminal groupsare exposed and contribute to effective killing.

The catalyst system may include as metallocene a compound of the generalformula

    R L M (D)

wherein M is a transition metal of group III B, IV B, V B, VI B of theperiodic table, wherein R is a ligand having a conjugated electronbonded to M of which there may be one, two or three such ligand whichmay be same of different;

wherein L is a leaving group preferably anionic bonded to M of whichthere may be one, two, three or four depending on the valency of M andthe member of other substituents on M; and

D is an optional electrondonating hetero atom group.

R may be or include a substituted or unsubstituted cycloalkadienyl groupsuch as cyclopentadiene, indenyl, tetrahydro-indenyl or fluorenyl. Wheremore than one such cycloalkadienyl group is present, the groups may bebridged (See Exxon EP 129368). Where only one cycloalkadienyl group ispresent such group may be bridged to other transition metal ligands suchas D (See EP 416815 and EP 420436).

L may be or include an aryl group, alkyl group, an aralkyl group, analicyclic group, a halogen atom, a hetero atom containing ligandcontaining an oxygen sulfur, nitrogen or phosphorus atom; these groupsmay be connected by single or multiple bonds to M.

The cycloalkadienyl group hence includes polycyclic structures.

The other catalyst component, generally alumoxane, may be prepared in apre-reaction and then introduced into the polymerisation system but mayalso be formed wholly or partly in situ by reaction of water and atrialkylaluminum, preferably trimethylaluminum. In EP 308177 water maybe introduced in the monomer feed for this purpose. The Al/transitionmetal mol ratio may be less than 10000, suitably from 10 to 5000,preferably from 50 to 2000, especially from 200 to 1500.

The killer components may be added separately or together. To maximiseeffectiveness at the separation stage, they are best added downstream ofthe polymerization zone before separation, preferably at a high pressureportion upstream of a pressure let-down valve or immediately downstreamat a lower pressure portion. Preferably the killer components are addedtogether in admixture. Advantageously the contact time between killercomponents and polymer before separation is at least 10 seconds,especially at least 20 seconds.

While many of the killer components listed above can be dissolved intoinert hydrocarbon solvents, this is not the case with water.

Thus in a further preferred aspect of the invention it has been foundthat along with water, the second non-volatile killer component can beselected so as to provide a largely homogeneous solution or asufficiently stable emulsion in an inert carrier liquid, permittingpumping of the killer components into the system at accuratelycontrolled levels without fouling or plugging of an injection pump orinjection line.

In this further aspect of the invention there is hence provided amixture of from 0.005 to 20 wt %, preferably from 0.025 to 10 wt % ofwater and an oxygen or nitrogen containing surface active agent such asglycerol mono-oleate (GMO) or sorbitol mono-oleate (SMO) preferably inan amount of from 0.05 to 90 wt % especially 1 to 50 wt % in an organicsolvent such as heptane for use as a catalyst killer.

Surprisingly, at a mixture of water and GMO at a weight ratio of H₂O/GMO of 1:20 can be solubilized completely by the GMO, forming a clearsolution.

This solution remains clear when diluting the H₂ O/GMO mix with solvent.The solution preferably contains from 50 to 95 wt % of solvent. Thesolution may be stable at ambient temperatures.

For appropriate polymerisation processes from 2 to 8% of water and 98 to92% of GMO or SMO by weight of water and GMO/SMO may be used. The amountof GMO or SMO can be reduced for high comonomer polymerisation.

The process may be used for polymerising ethylene or higher olefins suchas propylene, 1-butylene with or without modifier such as H₂, with orwithout higher molecular weight comonomers such as propylene, butyleneand/or other ethylenically unsaturated comonomers having from 3 to 20carbon atoms, preferably having up to 10 carbon atoms. The high catalystactivity which is preserved by the process of the invention also permitsthe incorporation of polyenes such as C₄ to C₁₂ dienes includingbutadiene, isoprene or 1,4 hexadiene which are not easily incorporated.The process also facilitates production of polymers containing highcomonomer levels under economically viable conditions. Polymerisationconditions (temperature; pressure) may vary depending on the monomersand the desired polymer product characteristics. The invention isapplicable wherever a direct monomer recycle without or with minorfacilities for catalyst poison removal takes place in the polymerisationof olefins following a separation of a polymer/monomer mixture. Pressuremay vary for example from 50 to 3500 bar.

Both aspects of the invention contribute to the establishment ofcontrollable killing conditions with minimal impact on polymerisation.

The improved process conditions may lead to a more homogeneous polymerproduct and narrower molecular weight distribution. With narrowercompositional distributions, narrow DSC melting peaks may be observed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram for the introduction of catalyst kill agentsinto a polymerisation process.

EXAMPLES 1-7

The polymerizations in Examples 1 to 7 were carried out (See FIG. 1) ina high-pressure continuous polymer production facility, at reactionpressures ranging from 1300 bar to 1600 bar and a polymerisation reactoroutlet temperature of from 140° to 220° C.

The facility has downstream of the polymerisation reactor 2 a letdownvalve 4 for reducing the pressure. Downstream of the valve there islocated a catalyst killer injection point 7. Heat exchangers 6 allowheating or cooling of the mixture emerging from reactor.

Downstream of the exchanger, there is provided a high pressure separator8 (HPS) for separating the monomer/polymer mixture. The polymer richphase is taken from the HPS for further processing; the monomer richphase is recycled to the reactor via the high pressure recycle system 10consisting of a series of coolers, polymer knockout vessels (forremoving low molecular weight residues) and a high pressure compressorwhich supplies the monomer feed to the polymerisation reactor.

Fouling in the high pressure recycle system is monitored by measuringthe pressure drop between the HPS and a suction (inlet) vessel of thehigh pressure compressor.

Post-reactions in the HPS are monitored by measuring the temperaturebetween the monomer and polymer outlet of the HPS. This is referred toas the outlet temperature spread. It is assumed that the catalyst systemin the polymer phase is deactivated sufficiently completely when theexothermic polymerisation is suppressed and the temperatures at bothoutlets are substantially the same.

Preparation of Catalyst Killer

Three catalyst killer mixtures were prepared:

Recipe No 1 (a decomposable volatile killer component):Di-tert.butylperpivalate is diluted with iso-octane (Isopar C) to a 3 wt% solution.

Recipe No 2 (a non-volatile and a decomposable volatile killer componentcombination):

1 weight part of glycerol mono-oleate (GMO) is heated to 40° C. anddiluted with 1 wt part of iso-octane. The mixture is agitated until ahomogeneous solution is obtained. This solution is then blended with 8wt parts of a premix of 3.1 wt % di-tert. butylperpivalate iniso-octane.

Recipe No 3 (a waterbased volatile/non-volatile catalyst system killercombination):

1 weight part of glycerol mono-oleate is diluted with 1 weight part ofiso-octane and agitated at 40° C. Then 0.05 wt parts of demineralizedwater is added and the warm mixture is agitated until a clear solutionis obtained. This solution then is diluted further by adding 8 wt partsof iso-octane.

                                      TABLE 1                                     __________________________________________________________________________    Operating Experience with Different Catalyst Killers                                                                           CAT                                                                     Induction                                                                           ACTIVITY                     Ex-       Cat-        Reactor        HPS   Period for                                                                          gr polymer/                  am-       a- KILLER   Outlet                                                                             HPS  HPS  Outlet                                                                              Polymeri-                                                                           gr transition                ple                                                                              Comonomer/                                                                           lyst   Mole Temp.                                                                              Press.                                                                             Offgas                                                                             Temp. sation in                                                                           metal  POLYMER               No Modifier (1)                                                                         (2)                                                                              TYPE                                                                              Ratio (3)                                                                          °C.                                                                         bar  Temp °C.                                                                    Spread, °C.                                                                  recycle, hrs                                                                        compound                                                                             Appearance            __________________________________________________________________________    1  Hydrogen                                                                             A  No 1                                                                              0.06/0                                                                             160-220                                                                            195-200                                                                            190-200                                                                            >30         10-20000                                                                             Coloured,                                                                     partly black          2  Hydrogen +                                                                           B  No 1                                                                              0.06/0                                                                             180  195-200                                                                            190-200                                                                            >30         10-20000                                                                             Coloured                 Propylene                                            partly black          3  Propylene                                                                            B  No 1                                                                              0.10 140-160                                                                            195-200                                                                            190-200                                                                            10-40 4-8   30-60000                                                                             Grey, sticky          4  Propylene                                                                            B  No 2                                                                              0.08/0.16                                                                          140-160                                                                            195-200                                                                            190-200                                                                             <5   4-8   Max 280000                                                                           Colourless,                                                                   dry                   5  Propylene                                                                            B  No 3                                                                              0.25/0.25                                                                          140-160                                                                            195-200                                                                            190-200                                                                             <3   >40   Max 360000                                                                           Colorless,                                                                    dry                   6  Hydrogen                                                                             B  No 3                                                                              0.15/0.15                                                                          160-180                                                                            195-200                                                                            190-200                                                                            <10         >80000 White                 7  Butene-1                                                                             B  No 3                                                                              0.18/0.18                                                                          140-160                                                                            195-200                                                                            190-200                                                                             <3   >80   Max 230000                                                                           Colourless,                                                                   dry                   __________________________________________________________________________     NOTES:                                                                        (1) Primary monomer is ethylene in all cases.                                 (2) Catalyst A = dicyclopentadiene zirconium dichloride                       Catalyst B = dimethylsilyl bis tetrahydroindenyl zirconium dichloride         Cocatalyst in all cases methylaluminium oxane supplied by Schering AG,        Bergkammen. Molar ratio aluminium/transition:metal compound = 100 in case     of catalyst A and = 420 for catalyst B.                                       (3) Mol ratio volatile component to aluminum on left; Mol ratio               nonvolatile component to aluminum on right.                              

EXAMPLE 1 (comparative)

Ethylene was polymerized in the presence of 1 to 10 mol % hydrogen withcatalyst A and a Al/Zr mole ratio of 100. Tertiary butyl perpivalatedissolved in iso-octane (Recipe 1) was used as catalyst killer. Thekiller/transition metal mole ratio was varied in a range from 3 to 6,equivalent to a killer/total metal mole ratio of 0.03 to 0.06. The totalmetal mole ratio is calculated on a combination of the molar amounts ofZr and the Al of alumoxane. Polymerization conditions were changed from160° to 220° C. The catalyst activity varied in the course ofpolymerisation and was found to be in the range 10 to 20000 g PE/g Zrcompound.

Waxes with a broad molecular weight distribution and strongly coloredfrom yellow to black were obtained. The polymer outlet temperature atthe high pressure separator was found to be 30° to 50° C. higher thanthe monomer outlet temperature, leading to the conclusion thatsubstantial post-reactions take place in the HPS. Temperature spreadsbetween the polymer and gas outlet as high as 80° C. were observed.Occasional black spots and cross-linked domains were found in the waxproduct.

Plugging was observed usually after a few hours in the complete recycleloop including in the reactor feed line.

EXAMPLE 2 (comparative)

Polymerisation conditions were as in example 1, but with approx 30 wt %propylene in reactor feed. Catalyst A was replaced by catalyst B. Thesame qualitative observations were made as described with example 1.

EXAMPLE 3 (comparative)

Propylene was used as comonomer with ethylene. Feed composition wasvaried in the range 70 to 85 wt % propylene, the reactor pressure was inthe range 1300-1500 bar and the reaction temp. was varied from 140° to160° C. Tertiary butyl perpivalate (Recipe 1) was added as a catalystkiller in a 0.06-0.10 mole ratio with respect to the total of aluminiumand transition metal.

With increasing killer flow rate it was found that the temperatureincrease in the high pressure separator could be reduced from typically25° to 40° C. to not lower than typically 10°-20° C. Thus post reactionswere taking place, as confirmed by GPC (gel permeation chromatography)to generate 2 to 5% of low molecular polymers which tend to bloom out ofthe polymer produced and create a sticky polymer surface. Usuallychanges in the killer flow rate were observed to affect the catalystconsumption (which is adjusted to obtain the desired equilibrum reactiontemperature after a time period equivalent to the residence time of themonomer recycle system) indicating that killer or killer residuessuppress or interfere with the action of the catalyst system.

The strongest impact on catalyst activity was observed at 0.10 killingratio which indicates that significant quantities of killer componentswere carried over to the reactor. As a result fairly low catalystactivities were obtained causing a grey product colour.

Although catalyst poisons were apparently recycling to the reactor,polymer formation in the monomer recycle system was observed causing thepressure drop to increase after 4 to 8 hours from initially <15 bar tomore than 20 bar. Polymers removed from the monomer recycle were foundto be different from the reactor product in terms of molecular weight,molecular weight distribution and crystallinity indicating that thesepolymers have been generated locally by still active catalyst.

Increasing conventional killer concentrations did not permit a goodcompromise between the need to kill catalyst in the HPS and yet notinterfere with catalyst activity in subsequent polymerisation.

EXAMPLE 4

Reaction conditions were similar to example 3. Glycerol mono-oleateaccording to recipe 2 was added to the killer component used in example3. Compared to example 3 the post reactions in the separator were foundto be substantially reduced as indicated by an HPS outlet spread of lessthan 5° C. at any killing ratio. The low molecular weight fraction ofthe polymer was decreased substantially and stickiness was greatlyreduced.

The catalyst activity reached about 5 times the value of example 3 atequivalent perpivalate/total metal mole ratio of 0.07-0.08 and with thenon-volatile GMO/total metal mole ratio at 0.14 to 0.16.

Similar to example 3 an increase of the pressure drop was observed aftera few hours due to local polymerisation.

EXAMPLE 5

The reaction conditions were similar to examples 3 and 4. The catalystkiller had been prepared by dissolving GMO and water in approximately a1:1 mole ratio according to recipe 3. The killer flow rate was adjustedto a point such that an impact on catalyst activity just becameapparent.

It was found that substantially higher molar quantities of volatilekiller could be injected as compared to example 3 and 4 withoutnegatively affecting the catalyst activity. The catalyst activityreached a value of 360.000 g PE/g Zr metallocene compound. Post-reactionin the HPS appeared essentially eliminated.

EXAMPLE 6

Polymerisation conditions similar to example 1, but employing a catalystof type B and killer Recipe 3 were used instead of catalyst A and killerrecipe nr 1. The monomer was ethylene only with H₂ as modifier to reducethe molecular weight. Post reaction in the HPS was reduced by a factorof 3 to 10 relative to Example 1 depending on catalyst killer ratio. Notemperature runaway reaction were observed at any liquid level up in theHPS. Polymer present in recycle coolers exhibited a lower viscosity thanthe wax product suggesting that these are low molecular weight productsextracted from the HPS and not polymer formed in situ in the coolersfrom monomer and still active residual catalyst. Catalyst activity wasat least 4 times as high as during the runs described under example 1.The wax product was completely white.

EXAMPLE 7

At reaction conditions similar to example 3 propylene was replaced bybutene-1. The same catalyst killer formulation was applied as withexample 5, i.e. GMO and H₂ O in a 1:1 mole ratio. Slight losses incatalyst activity became apparent at somewhat lower killing ratios thanwith propylene in example 5. Polymerisation in the recycle system wasnot observed after running a continuous polymerisation for 80 hours.High catalyst activity was observed.

EXAMPLES 8-14

Recipe No. 4

15 to 25 gr of GMO is dissolved into 5 Ltr. of Isopar C at 40° C. Then50 ml H₂ O are added under intensive agitation forming an unstableemulsion. The emulsion is kept in an agitated vessel and is transferredto the high pressure metering pump by means of a pump-around system inorder to maintain constant composition during injection.

Recipe No. 5

Same as recipe No. 4 except that 15 gr of Sorbitol monoleate is used inplace of GMO.

Recipe No. 6

Pure water.

EXAMPLES 8 and 9

Ethylene and an excess of butene-1 were copolymerized with a catalyst Band a commercially available MAO, delivered by Schering, Bergkamen, in amolar aluminum/transition metal ratio Al/TM=420. Initially a catalystkiller according to recipe No. 3 was injected at a relatively low molarratio H₂ O:GMO:Al 32 0.06:0.06:1.

Post reaction in the high pressure separator at these conditions werenegligible (Example 8).

While maintaining constant reaction conditions the killer No. 3 wasreplaced by pure water dispersed into an aromatic carrier fluid withdensity close to the density of water. The killer injection rate wasincreased successively until a level was reached where the postreactions in the HPS stopped. Over a 2 hours time period the catalystconsumption was found to decrease steadily and to level out at less thanhalf of the original consumption, equivalent to more than twice theoriginal catalyst productivity (Example 9).

EXAMPLE 10

Example 10 represents running conditions over several to more than 100hours of prolonged uninterrupted polymerization using different batchesof commercially available MAO from Schering, Bergkamen. Unconverted TMAin the MAO's ranged from 0.25 mole TMA/mol Al to 0.46 mol/mole.

The H₂ O/Al ratio was optimized by varying the killer injection rateuntil catalyst productivity started to decrease. H₂ O/Al ratios of 0.9mole/mole were possible in continuous operation with the 25% TMAcontaining MAO; the H₂ O/Al ratio was 1.2 with the TMA rich MAO.

EXAMPLE 11, 12

Example 11 and 12 are polymerization runs with hexene-1 being used ascomonomer.

The catalyst formulation is the same as in the previous examples.

EXAMPLE 13

The transition metal compound was di-(methylcyclopentadiene)zirconiumdichloride to provide low molecular weight polymer. Cocatalystis as in the previous examples.

EXAMPLE 14

As a catalyst system a bridged mono-Cp transition metallocene compoundand a MAO with 15% unconverted TMA was used. The metallocene has thegeneral formula: ##STR1##

EXAMPLE 15, 16

These Examples are performed on a different apparatus with addition of anon-volatile killer (water) only inside the reactor upstream of thelet-down valve.

The reactor arrangement was as follows:

A reactor has a stirrer and is divided in its reactor interior intozones. A gap is provided between the zones which governs the extent ofbackflow between the zones.

Monomer fed is fed principally to the initial part of the reactor, butminor amounts are fed downstream to complete the polymerizationreaction. Water is injected in the final zone which is referred to asthe killing zone.

For the test performed which are summarised in Table 1 a 50/50 mol %monomer/comonomer mixture was introduced without hydrogen as transferagent using the comonomers indicated in Table 1. The temperature of thefeed introduced was 50° C. A total residence time was approximately 100seconds, of which 15 seconds in the killing zone was provided.

Catalyst in the form of metallocene and cocatalyst was introducedupstream of the killing zone. Metallocene selection was as set out inTable 2. The Al/TM ratio was as set out in Table 2. The MAO used wasobtained by ageing a 30 wt % MAO solution in toluene and diluting itwith Isopar C (Registered TradeMark) to give an ultimate 7 wt %concentration of MAO in slurry form in a toluene/Isopar C blend.

Water was injected into the final killing zone until a light decrease incatalyst system productivity (the inverse of catalyst consumption) wasnoted. In Example 15 polymerisation conditions stabilised at a catalystconsumption of 0.00053 wt parts of solution per 1 wt part of monomerfeed. The water addition stabilised at 0.4 g H₂ O per g of MAO.

The temperature in the killing zone was from 180° to 190° C. gave aconversion of 11-12 wt % of the monomer/comonomer feed into polymer.

Approximately 9-10 wt ppm of water was present in the recycled feedsuggesting that approximately half of the water injected reacted withaluminium component and is removed with the polymer.

The polymer obtained had a MI of 4.5, a Mw of 70000, a density of 0.910containing 11 wt % of butene-1 comonomer. The Mn/Mw ratio was 2.1 and anarrow compositional distribution resulted.

By optimising the run conditions lower water injection levels and highermetallocene activities can be obtained.

Advantages of this process include also that monomer flashed off in alow pressure separator can be easily purified by single-stagefractionation for removing waxes and be re-compressed without requiringremoval of killer component. Also the monomer/comonomer feed may containwater.

                                      TABLE 2                                     __________________________________________________________________________    Examples 8 to 15                                                              __________________________________________________________________________                       KILLER                                                                            Mole Reactor                                                                            Reactor                                                                            Polymer wt %                            Example                                                                            Comonomer                                                                            Metallocene/                                                                         Recipe                                                                            Ratio                                                                              Press.                                                                             Outlet                                                                             Comonomer                               No   (1)    Al/TM ratio                                                                          No  H.sub.2 O/Al                                                                       BAR  TEMP.                                                                              Incorporation                           __________________________________________________________________________     8   Butene-1                                                                             B      3    0.06                                                                              1300 180  12.5                                     9   Butene-1                                                                             B      6   0.8-1.2                                                                            1300 180  12.4                                    10   Butene-1                                                                             B      4/5 0.9-1.2                                                                            1300 175  11.0                                    11   Hexene-1                                                                             B      5   0.8  1300 200  3                                            Hydrogen                                                                 12   Hexene-1                                                                             B      5   0.8  1350 170  14.0                                    13   Butene-1                                                                             C      5   0.5  1350 160  45                                      14   Butene-1                                                                             D      4   0.7  1300 165  31                                           Hydrogen                                                                 15   Butene-1                                                                             B-1    6   1.0-1.3                                                                            1300 190  10.8                                    __________________________________________________________________________                   Polymer   Polymer                                                                            HPS      Catalyst                                              Melt Index                                                                              Viscosity                                                                          Temp.    Activity                                         Example                                                                            gr/10 min CP at                                                                              Spread                                                                            Recycle                                                                            gr PE/                                           No   2.16 hl/190° C.                                                                  140° C.                                                                     °C.                                                                        Fouling                                                                            gr TM Comp.                            __________________________________________________________________________               8   5.5            N/D       47 000                                           9   4.8            N/D N/D  105 000                                          10   2.5-4          N/D N/D  100-350 000                                      11   10             N/D N/D  150 000                                          12   2.0            N/D N/D  >250 000                                         13   --        400  N/D N/D   70 000                                          14   10             N/D N/D   50 000                                          15   4.5            N/D N/D  400-800 000                            __________________________________________________________________________     N/D = NOT DETECTABLE.                                                         B = dimethylsilyl tetrahydroindenyl zirconium dichloride at Al/Zr mole        ratio of 420.                                                                 D = See text for metallocene, at Al/Zr mole ratio of 1400.                    C = See text for metallocene, at Al/Zr mole ratio of 400.                     B1 = As B but at Al/Zr mole ratio of 1000.                               

What is claimed is:
 1. Process for preparing olefinic polymerscomprising the steps of:(a) continuously feeding olefinic monomer and acatalyst system of a metallocene component and a cocatalyst component toa reactor; (b) continuously polymerising the monomer in the reactorunder elevated pressure in a polymerisation zone; (c) continuouslyremoving a monomer/polymer mixture from the reactor; (d) continuouslyseparating inonomer from polymer to form a monomer-rich and apolymer-rich phase; and (e) recycling separated monomer to the reactor,said process being characterised in that: (f) a volatile catalyst systemkiller component and a non-volatile catalyst system killer component areadded to suppress polymerisation outside of the polymerisation zone. 2.Process according to claim 1 in which the non-volatile killer componentis added in a molar ratio of from 0.01 to 10 of non-volatile killercomponent per mol of metal (metallocene and cocatalyst).
 3. Processaccording to claim 1 or 2 in which the non-volatile killer component isan oxygen containing compound.
 4. Process according to claim 1 or 2 inwhich the volatile killer component is water.
 5. Process according toclaim 1 in which the volatile and non-volatile components are mixed forcommon introduction, preferably in the form of a solution or emulsionwhich may be formed with the aid of additional solvent.
 6. Processaccording to claim 1 in which at least the volatile component is addedin a killer reaction zone upstream of a high pressure letdown valve. 7.Process for preparing olefinic polymers comprising the steps of:(a)continuously feeding olefinic monomer and a catalyst system of ametallocene component and a cocatalyst component to a reactor; (b)continuously polymerising the monomer in a polymerisation zone in thereactor under elevated pressure; (c) continuously removing amonomer/polymer mixture from the reactor; (d) continuously separatingmonomer from molten polymer at a reduced pressure; and (e) recyclingseparated monomer to the reactor, characterised in that: (f) water isadded as a volatile catalyst system killer component to suppresspolymerisation outside of the polymerisation zone.
 8. Process accordingto claim 7 in which the cocatalyst component includes an aluminum alkylcapable of hydrolising with excess water to produce alumoxane. 9.Process according to claims 7 or 8 in which there is no addition of anon-volatile catalyst system killer component.
 10. Process according toclaim 7 in which water is added in amounts such that the catalyst systemis killed sufficiently to permit polymer separation, unreacted waterbeing recycled with separated monomer.
 11. Process according to claim 7in which water is added into a killer reaction zone upstream of a highpressure let-down valve or downstream of a high pressure let-down valve.12. Process according to claim 11 in which the killer reaction zone isdefined by a baffle in a high pressure reaction vessel with apolymerization zone upstream of the killing reaction zone and isupstream of the pressure let-down valve.
 13. Process according to claim7 in which monomer and residual water are removed from a low pressureseparator and recycled from the low pressure separator withoutadditional separate water removal for feeding to the reactor. 14.Process according to claims 1 or 7 in which the metallocene is used inan amount of 0.01 to 100 g of metallocene per 10⁶ g of monomer. 15.Process according to claim 8 in which water is added as a catalystsystem killer component at a molar ratio of 0.005 to 2.5 mole of waterper mol of total metal in the catalyst system.
 16. Process according toclaim 1 in which the volatile killer component and non-volatile killercomponent are added downstream of the polymerization zone and upstreamof a means for separating monomer from molten polymer.
 17. Processaccording to claim 2 in which the non-volatile killer component is addedin a molar ratio of from 0.05 to 2 of non-volatile killer component permol of total metal in the catalyst system.
 18. Process according toclaim 5 in which the mixture of volatile and non-volatile components isintroduced downstream of a high-pressure let-down valve.
 19. Processaccording to claim 18 in which the mixture of volatile and non-volatilecomponents is introduced upstream of a high pressure separating stage.20. Process according to claim 7 in which the water is added downstreamof the polymerization zone and upstream of a means for separatingmonomer from molten polymer.
 21. Process according to claim 10 in whichthe catalyst system contains a component capable of reacting withunreacted water.
 22. Process according to claim 14 in which themetallocene is used in an amount of from 0.1 to 10 g/10⁶ g of polymer.23. Process according to claim 15 in which the water is added at a molarratio of 0.05 to 1.5 mol of water per mol of total metal in the catalystsystem.
 24. Process for preparing olefinic polymers comprising the stepsof:(a) feeding olefinic monomer and a catalyst system of a metallocenecomponent and a cocatalyst component to a reactor; (b) polymerising themonomer in the reactor under elevated pressure in a polymerisation zone;(c) removing a monomer/polymer mixture from the reactor; (d) separatingmonomer from polymer to form a monomer-rich and a polymer-rich phase;and (e) recycling separated monomer to the reactor, said process beingcharacterised in that: (f) a volatile catalyst system killer componentand a non-volatile catalyst system killer component are added to killpolymerisation outside of the polymerisation zone.
 25. Process forpreparing olefinic polymers comprising the steps of:(a) feeding olefinicmonomer and a catalyst system of a metallocene component and acocatalyst component to a reactor; (b) polymerising the monomer in apolymerisation zone in the reactor under elevated pressure; (c) removinga monomer/polymer mixture from the reactor; (d) separating monomer frommolten polymer at a reduced pressure; and (e) recycling separatedmonomer to the reactor, characterised in that: (f) water is added as avolatile catalyst system killer component to kill polymerisation outsideof the polymerisation zone.
 26. Process according to claim 3 in whichthe non-volatile killer component contains a terminal hydroxy group. 27.Process according to claim 1 in which the non-volatile killer componentis a nitrogen containing compound.
 28. Process according to claim 1 inwhich the non-volatile killer component is a sulfur containing compound.29. Process according to claim 1 in which the non-volatile killercomponent has a molecular weight higher than
 200. 30. Process accordingto claim 29 in which the non-volatile killer component has a molecularweight higher than
 300. 31. Process according to claim 1 in which thevolatile killer component is an oxygen containing compound.
 32. Processaccording to claim 1 in which the volatile killer component is anitrogen containing compound.
 33. Process according to claim 1 in whichthe volatile killer component is a sulfur containing compound. 34.Process according to claim 1 in which the volatile killer component hasa molecular weight less than
 200. 35. Process according to claim 34 inwhich the volatile killer component has a molecular weight less than 80.